The present invention relates to a pneumatic tire having better aerodynamic characteristics than conventionally-shaped tires.
Wind tunnel tests have indicated that at a steady speed of 100 kilometers per hour air drag accounts for about 75 percent of the fuel consumption of a typical passenger automobile, with conventionally-shaped tires mounted on the automobile contributing about 10 percent of the total air drag on the automobile. The external contour of a radial cross-section of a conventionally shaped tire mounted on a rim and not subjected to a load has a maximum diameter at the mid-circumferential centerplane of the tire, a maximum axial width that is greater than the axial distance between the retaining flanges of the rim at a location somewhere between the rim and the maximum diameter of the tire, and an axial width adjacent to the retaining flanges of the rim that is about 70 to 85 percent less than the tire's maximum axial width.
As used herein and in the appended claims: "axial" and "axially" refer to directions that are parallel to the axis of rotation of a tire, or tire and rim assembly; "radial" and "radially" refer to directions that are perpendicular to the axis of rotation of a tire, or tire and rim assembly; and "the mid-circumferential centerplane" of a tire is a plane that is perpendicular to the axis of rotation of a tire, or tire and rim assembly, and is located midway between the external surfaces of the sidewalls of a tire at its maximum axial width exclusive of ornamentation or indicia.
The aerodynamic characteristics of a pneumatic tire may be improved by providing the tire with an external contour which accelerates the flow of air smoothly from the mid-circumferential centerplane to the junction of the tire sidewall with the flanges of a rim that the tire is mounted upon. In order to attain such a smooth acceleration of the air flow, the external contour of the tire should not present any abrupt or sharp changes in axial direction. The significant difference between the axial width of a conventionally-shaped tire at the rim flanges and at its point of maximum axial width may result in air flow separation, turbulence, and drag as the flow of air attempts to follow the contour of the tire sidewall.
The desirability of streamlining tires and rims for use on aircraft was recognized several years ago, with such tires being described, for example, in U.S. Pat. Nos. 2,005,626 and 2,052,130. The aircraft tire described in U.S. Pat. No. 2,005,626 is a low pressure tire which is intended to have a streamlined shape and minimum air flow resistance in flight only, since it deforms to increase in ground-contacting area when the tire is under load. U.S. Pat. No. 2,052,130 discloses a tire having a cross-sectional profile substantially conforming to a segment of an ellipse, and as a result it presents a narrow surface for engagement with the ground, in comparison with the overall width of the tire, so that the traction and handling characteristics of such a tire on a surface vehicle would not be very satisfactory by today's standards. However, a tire according to the present invention not only has improved aerodynamic characteristics, but also meets the handling and traction requirements of modern surface vehicles.